PH EFFECTS ON THE SPECTROSCOPIC AND PHOTOCHEMICAL BEHAVIOR OF ENOXACIN - A STEADY-STATE AND TIME-RESOLVED STUDY

The spectroscopic and photochemical behavior of Enoxacin (ENX), oxo-7- (1-perazinyl)-1,8-naphthyridine-3-carboxylic acid, has been investigat ed in aqueous solutions between pH 3.5 and pH 12. The absorption and e mission properties of ENX are strongly affected by pH. The fluorescenc e quantum yield, 4 x 10(-3) at pH 3.5, increases by a factor of two on going to neutral pH while a strong reduction is observed at alkaline pH, The photodegradation quantum yield also depends on pH, being maxim um in neutral conditions (ca 0.04). Nanosecond flash photolysis experi ments confirm that the yield of absorbing transients is maximum at neu tral pH while it decreases to zero at acid and alkaline pH, These resu lts indicate that both the dissociation of the carboxylic group and th e protonation of the piperazinyl residues are key steps for the format ion of the photochemically active form of ENX. Loss of F- by heterolyt ic cleavage of the C-F bond is proposed to occur from the triplet stat e of the zwitterion with formation of a carbocation, A path for the ev olution of this intermediate to the final product. is also proposed.